While Irma’s extreme winds have been impressive and have caused catastrophic damage on the islands it has passed over, their effect on the ocean may be even more catastrophic once it gets close to Florida and the East Coast. The combination of low pressures and high wind speeds causes a dome of ocean water to grow near the center of circulation and pile up against whatever shore is in its way. With strong onshore winds, the amount of water that will be driven inland could be phenomenal. Unlike Harvey, where the flooding was freshwater due to the incredible rains, storm surge is primarily wind- and pressure-driven ocean water that floods into coastal areas. Since water is so heavy, it can cause tremendous damage in its path, leaving a “bathtub ring” of destruction behind. Depending on the path that Irma takes, we could get storm surge on Florida’s west coast, east coast, or potentially even both coasts at once if it goes right up the middle of the state.
Why is this particularly important in this storm? Because three of the top four most vulnerable areas to storm surge in the US are located in Irma’s forecast cone. Hurricane Hal’s Storm Surge blog, written by Dr. Hal Needham, discusses the historical oddity of the “Protected Coast” in northeast Florida and Georgia, where hurricanes rarely hit, in this 2016 entry. In this 2017 article on Harvey, he also discusses the most vulnerable areas for storm surge in the US, including Georgia/southern South Carolina, Palm Beach/Fort Lauderdale, and Florida’s West Coast, especially Tampa/St. Pete.